Ion sensor

ABSTRACT

A portion of a board (1) on which copper wiring is printed is provided with a carbon coating, the board (1) and lead wires (2) are joined by solder (3), the portion having the solder (3) is insulated with a silicone resin (4), and the carbon-coated printed wiring portion (10a) is successively coated with a redox layer (11) obtained by electro-oxidation of 2,6 xylenol and an ion-selective layer (12), thereby forming an ion sensor (20). 
     Since the ion sensor can be formed on a printed wiring board, various devices which include an ion sensor can readily be fabricated on a board.

This application is a continuation of application Ser. No. 415,331,filed as PCT/JP88/00143, Feb. 12, 1988.

TECHNICAL FIELD

This invention relates to an ion sensor and, more particularly, to anion sensor that uses a board on which an ion-sensitive portion isformed.

BACKGROUND ART

The inventors have filed applications for ion sensors employing a carbonelectrode (in which basal plane pyrolytic graphite carbon, namely BPGcarbon, glassy carbon or the like is used as the electrically conductivecarbon material) as a substrate, wherein the board is coated with aredox layer which may in turn be coated with an ion-selective layer.

With ion sensors so configured, however, there is a limitation upon theshape of the board and difficulties are encountered particularly inminiaturization and in utilizing the above-described art in circuittechniques involving semiconductors and the like.

In the future, sensor techniques employing ion sensors will not belimited to systems in which mere measurements are taken by using asensor. Since there will be a need to develop software in theelectronic, electrical, biological and fermentation fields and in thefield of medicine (clinical medicine, diagnosis, examination,communication, etc.), it will be required to develop sensor technologyin combination with sophisticated board technology.

DISCLOSURE OF THE INVENTION

The present invention provides an ion sensor using a board on which anion-sensitive portion is formed and which is utilizable in circuit boardtechnology as well.

As means for solving this problem, the ion sensor of the presentinvention is equipped with a board on which an ion-sensitive portion isformed, a carbon layer which includes carbon coating the ion-sensitiveportion, and a redox layer coating the carbon layer and exhibiting aredox function.

In this arrangement, an electric potential which corresponds to an ionconcentration is produced in the ion-sensitive portion formed on theboard.

In accordance with the present invention, there can be provided an ionsensor using a board on which an ion-sensitive portion is formed andwhich is utilizable in circuit board technology as well.

More specifically, in accordance with the present invention,

(1) ultrafine wiring can be coated with electrically conductive carbonin a simple manner, and it is possible to form the carbon boardconstructed of insulated wiring;

(2) the carbon board can be coated with a pin hole-free redox responsivemembrane by an electrooxidative reaction; and

(3) the ion sensor is of a composite membrane-type coated with anion-selective membrane.

Since a printed circuit board, namely a screen-printed board or asemiconductor circuit board, can readily be coated with theabovementioned membranes, this technique can be utilized in fields thatapply this sensor technology, e.g., in the electronic, electrical,biological and fermentation fields and in the field of medicine(clinical medicine, diagnosis, examination, communication, etc.).

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a prototypal view of a printed board used in a firstembodiment;

FIG. 2(a) shows an electrically conductive carbon electrode of the firstembodiment;

FIG. 2(b) shows a film board electrode of the first embodiment;

FIG. 3 is a view showing a circuit for measuring emf response in thefirst embodiment;

FIG. 4 is a view showing experimental results in the first embodiment;and

FIG. 5 is a structural view showing a handy ion sensor of a secondembodiment.

BEST MODE FOR CARRYING OUT THE INVENTION

Embodiments of the present invention will now be described in detail inaccordance with the accompanying drawings.

EXAMPLE 1

(1) As shown in FIG. 1, a board 1 was fabricated by applying, by meansof a brush, a single layer (membrane thickness: about 0.5 mm) of acarbon paste (viscosity: 150-300p_(s) ; JEF-010, manufactured by NihonAchison K. K.) to a portion A of a board (having a wire width of 0.1 mmat fine portions, manufactured by Mitsui Kinzoku Kogyo K. K.) obtainedby printing copper wiring on a polyimide film, and sintering the boardfor 30 min at a sintering temperature of 150° C. "JEF-010" (graphite) isa high quality electrically conductive ink primarily used for screenprinting. This material is characterized as follows:

Features:

1. Semi flexible-type conductive ink which enables printing circuitpatterns with its excellent electrical characteristics;

2. Scratching durability and wear resistance with minute particles ofgraphite being dispersed in a thermosetting binder;

3. Suitability for application to rigid substrate printing, contractprinting or circuit printing of separate membrane;

4. Solvent proof;

5. Moisture proof (70° C., 95% RH-240 hours);

6. Heat proof (max 200° C.);

Typical uses

1. Circuit printing of separate membrane;

2. Contact printing;

3. Potentiometer printing;

4. Terminal printing;

5. Keyboard Switch;

Specifications--Characteristics of Liquid

1. Electrically conductive particle: graphite

2. Binder: thermosetting resin;

3. Viscosity: 15,000-30,000 cps;

4. Density: 1.21 kg/l;

5. Effective period of storage: about 6 months under seal. Next, anelectrically conductive carbon electrode 10 shown in FIG. 2(a) wasfabricated by joining the board 1 and urethane-coated copper wires 2(lead wires) using solder 3, and insulating the soldered portion 3 witha silicone resin 4.

(2) A film board electrode 20 was fabricated by carrying out anelectro-oxidative reaction under the conditions given below to coat acarbon-coated printed wiring portion 10a of the electrically conductiveelectrode 10, which was fabricated in accordance with method (1), with aredox layer 11, and coating the resulting element with a hydrogen ioncarrier membrane 12.

With regard to the electro-oxidative reaction conditions, use was madeof a three-pole cell in which the abovementioned electrically conductivecarbon electrode 10 was employed as a working electrode, an SSCE as areference electrode, and a platinum mesh as a counter electrode.

Electro-oxidative reaction conditions

Electrolyte: 0.5M 2,6 xylenol, 0.2M sodium perchlorate acetonitrilesolvent

Electrolytic temperature: -20.0° C.

Electrolytic conditions: After the electrolytic potential was swepttwice from 0V to 1.5 V (vs. a saturated sodium calomel electrode) at ascan rate of 50 mV/sec, constant potential electrolysis was performed at1.5 V for 10 min.

Next, a proton carrier membrane serving as the hydrogen ion carriermembrane 12 was formed on the electrode surface by dipping under thefollowing conditions:

Proton carrier membrane composition

    ______________________________________                                        TDDA            313 mg   6 wt %                                               KTpClPB         31.3 mg  0.6 wt %                                             DOS             3255 mg  62.3 wt %                                            PVC             1625 mg  31.1 wt %                                            THF solution                                                                  ______________________________________                                    

Experiment 1

When the relationship between pH and the emf response of the film boardelectrode 20 was measured over a pH range of 5-9 in a standard buffersolution by the circuit shown in FIG. 4 using the film board electrode20, which was prepared as described above, and an SSCE electrode 21, theresults obtained showed a linear relationship, as illustrated in FIG. 3,with the slope of the straight line being 56.05 mV/pH (37° C.).

Thus, there was fabricated a sensor having a high possibility ofpractical use as a sensor capable of pH measurement with a printedwiring film (thin membrane).

EXAMPLE 2

A handy-type ion sensor 50 is shown in FIG. 5.

The ion sensor 50 receives an input of various analog data from a sensorinput unit 51 comprising an ion sensor electrode 51a, a referenceelectrode 51b, a common electrode 51c and a thermister 51d. These dataare converted into digital data by an A/D converter 52. On the basis ofthese data and in accordance with a program stored in a ROM 54, a CPU 53computes an ion concentration and outputs the same to an output unit 56while storing data in a RAM 55.

Though a handy-type ion sensor has been described as one example,various devices which include an ion sensor can readily be fabricated ona board by the technical concept of the present invention, and anapparatus capable of measuring a plurality of ion types simultaneouslycan be obtained. Furthermore, the invention paves the way forapplication to integrated circuitry and to devices in which integratedcircuits are coated with ion-selective layers.

Though a hydrogen ion carrier membrane is described as typifying the ioncarrier membrane in the present embodiment, similar results can also beobtained in other ion carrier membranes for anions such as calcium ion,potassium ion, sodium ion, magnesium ion and ammonium ion, as well asfor carbon ion, chlorine ion, phosphate ion, acetate ion and sulphuricacid ion. The same is true for gas sensors for oxygen, carbon dioxidegas and the like, and for biosensors such as enzyme sensors.

Though carbon paste was used as the carbon material in the embodiments,it is also permissible to use a carbon-containing toner, acarbon-containing emulsion or a carbon-containing electricallyconductive adhesive.

What is claimed is:
 1. An ion sensor comprising:a printed board on whicha plurality of conductive wires about 0.1 mm in width are closelyprinted; a plurality of sintered carbon layers each formed on one ofsaid conductive wires, said sintered carbon layers being made byapplying and sintering a carbon-containing paste including carbonparticles in thermosetting resin binder; and a plurality of redox layermade by an electrolytic oxidative polymerization process each coatingone of the sintered carbon layers and exhibiting a redox function.
 2. Anion sensor according to claim 1, further comprising a plurality ofion-selective layers each coating one of said redox layers andexhibiting ion selectivity.
 3. An ion sensor according to claim 2,wherein each of at least two different kinds of said ion-selectivelayers is formed on a different conductive wire.
 4. An ion sensorcomprising:a printed board on which a plurality of conductive wiresabout 0.1 mm in width are closely printed; a sintered carbon layerformed on one of said conductive wires, said sintered carbon layer beingmade by applying and sintering a carbon-containing paste includingcarbon particles in thermosetting resin binder; a redox layer made by anelectrolytic oxidative polymerization process coating said sinteredcarbon layer and exhibiting a redox function; and a reference electrode,a common electrode, a thermistor or a combination thereof formed on saidconductive wires adjacent to said one of conductive wires on which saidsintered carbon layer and redox layer are formed.
 5. An ion sensoraccording to claim 4, further comprising a ion-selective layer coatingsaid redox layer and exhibiting ion selectivity.